There are a few other remotes that understand Pronto Hex, but don't understand the ones that start with 5000, just the ones that start with 0000.

For those you can use the MakeHex program to generate the 0000 version of RC5.

The 0000 version of RC5 doesn't encode the "toggle bit" of the RC5 protocol, so you may end up with signals where each one works following any different one, but no signal works again immediately following itself. There are a variety of tricky work arounds for that. But first see how far you get without worrying about that detail.